1. Field of the Invention
The invention relates to a flame retardant polyolefin compound having low smoking and toxicity, and particularly to a low smoking and flame retardant material to be used as electric wire and cable covering materials or various electric part materials.
2. Description of the Related Art
Since polyolefin resins are generally flexible, excellent in electrical insulating properties, and cheaper than other materials, they have been used extensively as electric wire covering materials and various electric part materials. But, because of the past serious fires, the electric wire covering materials and various electric part materials are increasingly demanded to be flame-retardant, and such demands are becoming rigorous.
In response to such demands, a flame retardant using an organic halogen compound and antimony trioxide has been proposed and used. But, a flame-retarding material used in such a combination is partly decomposed to produce halogen gas in its production process, corroding its processing machine and molding machine, and also exerting toxicity to workers.
Besides, there is a disadvantage of producing a large quantity of smoke containing toxic gas in case of fire. Therefore, in view of safety in production and use, demands for non-halogen-based flame retardants have increased, and metal hydroxides are attracting attention.
But, aluminum hydroxide representative of the metal hydroxides starts to dehydrate at about 190.degree. C., causing a problem of bubbling in a molded article. Therefore, it has a disadvantage that its applicable resins are limited.
On the other hand, magnesium hydroxide decomposes at a high temperature and its applicable resins are substantially not limited, and it is now being used as a non-halogen-based flame retardant compound material for electric wire covering materials and various electric part materials.
However, since the polyolefin resin is generally flammable, and to make it flame retardant, it is required to add a large quantity of magnesium hydroxide, resulting in causing practical disadvantages that the intrinsic properties of the resin are deteriorated, and mechanical properties and processability are extremely deteriorated.
In order to remedy such disadvantages, it was tried to add a flame-retarding aids such as red phosphorus or fine carbon powder to a halogen-free polyolefin-based resin material to reduce the addition of hydroxide as low as possible. But, there were disadvantages that red phosphorus must be handled carefully when processing, and when fine carbon powder is added in a small amount to meet the mechanical properties, its effect as the flame-retarding aid is not attained.